M19-354
Page 14
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2019 AMETEK Brookfield Inc. All rights reserved.
\III. CALCULATIONS
III.1 Dynamic Viscosity
With Newtonian liquids absolute values of the dynamic viscosity are calculated, where as,
for non-Newtonian liquids, relative values of the dynamic viscosity (apparent viscosity) are
calculated.
The dynamic viscosity is calculated according to the following equation:
Equation 1:
η =
t(
ρ
1
-
ρ
2
)K
•
F
where:
η
dynamic viscosity [
mPa•s
]
t
traveling time of the ball [s]
ρ
1
density of the ball according to the test certificate [g/cm
3
]
ρ
2
density of the sample [g/cm
3
]
K ball constant according to test certificate [mPa·cm
3
/g]
F
working angle constant
Angle of inclination a
(applied to the level)
Working angle constant F
80° (DIN)
1.0
70°
0.952
60°
0.879
50°
0.778
The density and ball constant are each stated in the test certificate.
Consideration for buoyancy of the ball in the sample is accounted for by means of (
ρ
1
-
ρ
2
) in
equation (1).
The density of the sample can be determined by:
• referring to the material specifications from the manufacturer of the fluid
• measuring with a densitometer
Note:
Be sure to measure the sample density at the same temperature at which the viscosity
will be measured.
As
ρ
1
-
ρ
2
becomes small, a higher resolution on density measurement is required. The den
-
sity of the sample to be determined to 0.001g/cm
3
(3rd decimal position) for the glass balls and
0.01g/cm
3
(2nd decimal position) for the metal balls.
